1. Field of the Invention
The present invention relates to the catalytic isomerization of alpha-isophorone to beta-isophorone.
2. Discussion of the Background
Beta-isophorone is of great economic interest as a basic organic material for organic preparations, for example, in the perfume industry as well as a starting product for various vitamin syntheses. However, in the well-known trimerization of acetone the product is mainly alpha-isophorone in more than 90% yield. A high yield, simple conversion of the alpha-isomer to the beta-isomer is of particular interest, as it is possible to synthesize from the beta-isomer, natural products, which produce little or no problems in their effect or their degradation behavior.
The shifting of the double bond in the isophorone molecule resulting from the synthesis of alpha-isophorone produces great problems because
(1) the double bond must be shifted out of conjugation with the carbonyl group,
(2) the system easily reacts to stronger alkali or even acid catalysts with dehydration of the compounds and polymerization,
(3) the energy content of the molecule must be clearly raised and
(4) the adjustment of the equilibrium takes place only slowly.
Due to the relatively small amount of beta-isophorone existing at equilibrium, the continuous removal of the desired isomer causes considerable technical problems; however, it is not in each case a prerequisite for a practical procedure. As no changes can be made in the equilibrium for generally known thermodynamic reasons, it was possible only to attempt to influence the rate of the equilibrium adjustment without causing an increase in side reactions. ##STR1##
A number of methods for the preparation of beta-isophorone are known. However, all of these methods have considerable disadvantages, so that to date none of these methods can be converted into practice or utilized on a technically applicable scale. A molecular rearrangement can be produced, e.g., by the conversion of molar quantities of alpha-isophorone with methylmagnesiumiodide with the addition of iron(III)chloride, subsequent hydrolysis and distillative processing (A. Heymes and P. Teisseire, Recherches 1971, 18, 104-8). The isomerization also takes place upon several hours of boiling with triethanolamine, subsequent fractionation and washing of the distillate with tartaric acid and salt solution (Firmenich S. A., DE-OS No. 24 57 157). The conversion is also possible by catalysis with weakly dissociated organic acids. In one such procedure the yield is about 70% of pure beta-isophorone with the use of adipic acid (Hoffmann-La Roche & Co. AG, DE-PS No. 25 08 779).
All the known procedures have the disadvantage that either the use of large volumes of chemicals are required with the related reprocessing and waste disposal problems or that the catalysts used are too weakly alkaline or acidic to realize an acceptable space/time yield. A simple increase or reduction of the acidity of the catalyst is not possible as otherwise there is increased polymerization and dehydration by self-condensation of the isophorone.